Liquid crystal display devices utilize optical anisotropy and dielectric anisotropy of liquid crystalline compounds. As display mode of the devices, twisted nematic (TN) mode, super twisted nematic (STN) mode, dynamic scattering (DS) mode, guest-host (GH) mode, and DAP (Deformation of Aligned Phases) mode have been known. As driving mode for the display devices, static driving mode, time shearing addressing mode, active matrix driving mode, and two-frequency addressing mode have been known.
Liquid crystal compositions used for these liquid crystal display devices are required to exhibit liquid crystal phase at wide temperature range and to be stable against heat, light, moisture, air, electric field, and electromagnetic radiation. Accordingly, several kind of liquid crystal compounds are used in combination for display device materials. Sometimes, number of the liquid crystal compounds becomes more than 20 and therefore each of the liquid crystal compounds is required to be good in miscibility with other liquid crystal compounds. Particularly, since the display devices have recently come to be used in severe environments, improvement of miscibility at low temperatures has come to be required. Besides, in keeping with demand for display devices of higher qualities, improvements of liquid crystal compositions in the speed for responding to the change of electric field and in the steepness are required, and thus it has become necessary to control physical properties such as dielectric anisotropy and ratio of elastic constants to most suitable values depending on the display mode and the shape of the devices.
Another characteristic required of effective liquid crystal display devices is that the devices have a good display contrast and wide viewing angle. For this purpose, it is necessary to keep the product (.DELTA.n.multidot.d) of optical anisotropy (.DELTA.n) multiplied by cell thickness (d) at a constant value. One method for increasing the response speed is to reduce the cell thickness (d). Accordingly, in order to achieve this purpose while maintaining the product (.DELTA.n.multidot.d) described above at a desired value, liquid crystal compositions having high An are necessary and in order to produce such liquid crystal compositions, liquid crystalline compounds having high .DELTA.n become necessary.
As compounds having comparatively high .DELTA.n, tolan compounds expressed by the general formula (10) are disclosed in Laid-open Japanese Patent Publication No. Sho 61-5031, alkynyloxytolan compounds expressed by the general formula (11) are disclosed in Laid-open Japanese Patent Publication No. Hei 2-207056, alkynyltolan compounds expressed by the general formula (12) are disclosed in Laid-open Japanese Patent Publication No. Hei 2-180840, allylcyclohexyltolan compounds expressed by the general formula (13) are disclosed in Laid-open Japanese Patent Publication No. Hei 3-58944, and fluorotolan type alkenyl compounds expressed by the general formula (14) are disclosed in Laid-open Japanese Patent Publication No. Hei 5-65236, respectively. ##STR1##
wherein Rc represents an alkyl group having 1 to 8 carbon atoms,
Rd represents an alkenyl group having 2 to 14 carbon atoms, and PA1 X represents H or F. PA1 (1) A liquid crystalline alkenyltolan derivative expressed by the general formula (1) EQU C.sub.t H.sub.2t-1 --G--(CH.sub.2).sub.m --A.sub.1 --B.sub.1 --(A.sub.2 --B.sub.2).sub.n --(A.sub.3 --B.sub.3).sub.p --A.sub.4 --X (1) PA1 wherein A.sub.1, A.sub.2, A.sub.3, and A.sub.4 independently represent a 1,4-cyclohexylene, 1,4-phenylene in which one or two hydrogen atoms may be replaced by a fluorine atom(s), dioxane-2,5-diyl, or pyrimidine-2,5-diyl group; B.sub.1, B.sub.2, and B.sub.3 independently represent a covalent bond, an 1,2-ethylene, 1,2-ethenylene, 1,2-ethynylene, oxymethylene, methylenoxy, carbonyloxy, or 1,4-butylene group provided that at least one of B.sub.1, B.sub.2, and B.sub.3 represents an 1,2-ethynylene group; G represents a covalent bond or an oxygen atom; C.sub.t H.sub.2t-1 represents an alkenyl group having t carbon atoms wherein t is an integer of 2 to 10; m is an integer of 0 to 2; n and p are independently an integer of 0 or 1; X represents an alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a chlorine atom, a bromine atom, or a cyano group wherein one or more methylene groups or fluoromethylene groups in the alkyl group or the fluoroalkyl group may be replaced by an oxygen atom(s) or an 1,2-ethenylene group, but adjacent two methylene groups should not be simultaneously replaced by them; provided that when A.sub.4 represents 1,4-phenylene group which is not substituted with a fluorine atom(s), there is no case that G represents a covalent bond and t+m=3 simultaneously; and each element in the molecule may be its isotope. PA1 (2) The liquid crystalline alkenyltolan derivative recited in paragraph (1) above wherein n and p are 0. PA1 (3) The liquid crystalline alkenyltolan derivative recited in paragraph (1) above wherein n is 1 and p is 0. PA1 (4) The liquid crystalline alkenyltolan derivative recited in paragraph (1) above wherein n and p are 1. PA1 (5) The liquid crystalline alkenyltolan derivative recited in paragraph (2) above wherein X represents a chlorine atom, a bromine atom, a cyano group, or a fluoroalkyl group having 1 to 10 carbon atoms in which one or more fluoromethylene groups may be replaced by an oxygen atom(s) or 1,2-ethenylene group(s). PA1 (6) The liquid crystalline alkenyltolan derivative recited in paragraph (2) above wherein X represents an alkyl group having 1 to 10 carbon atoms in which one or more methylene groups may be replaced by an oxygen atom(s) or an 1,2-ethenylene group(s); and A.sub.1 and A.sub.4 independently represent a 1,4-phenylene group in which one or two hydrogen atoms may be replaced by a fluorine atom(s) PA1 (7) The liquid crystalline alkenyltolan derivative recited in paragraph (2) above wherein G represents a covalent bond, t+m=4, and a double bond exists at a terminal of the molecule. PA1 (8) The liquid crystalline alkenyltolan derivative recited in paragraph (2) above wherein G represents a covalent bond, t+m=5, and a double bond exists at a second position counting from a terminal of the molecule. PA1 (9) The liquid crystalline alkenyltolan derivative recited in paragraph (3) above wherein X represents a chlorine atom, a bromine atom, a cyano group, or a fluoroalkyl group having 1 to 10 carbon atoms in which one or more fluoromethylene groups may be replaced by an oxygen atom(s) or an 1,2-ethenylene group(s). PA1 (10) The liquid crystalline alkenyltolan derivative recited in paragraph (3) above wherein X represents an alkyl group having 1 to 10 carbon atoms in which one or more methylene groups may be replaced by an oxygen atom(s) or an 1,2-ethenylene group(s). PA1 (11) The liquid crystalline alkenyltolan derivative recited in paragraph (10) wherein G represents a covalent bond, t+m=4, and a double bond exists at a terminal of the molecule. PA1 (12) The liquid crystalline alkenyltolan derivative recited in paragraph (10) wherein G represents a covalent bond, t+m=5, and a double bond exists at a second position counting from a terminal of the molecule. PA1 (13) The liquid crystalline alkenyltolan derivative recited in paragraph (11) wherein B.sub.1 represents a covalent bond and B.sub.2 represents an 1,2-ethynylene group. PA1 (14) The liquid crystalline alkenyltolan derivative recited in paragraph (12) wherein B.sub.1 represents a covalent bond and B.sub.2 represents an 1,2-ethynylene group. PA1 (15) The liquid crystalline alkenyltolan derivative recited in paragraph (13) wherein A.sub.1 represents an 1,4-cyclohexylene group, and A.sub.2 and/or A.sub.4 represents an 1,4-phenylene group in which a hydrogen atom(s) may be replaced by a fluorine atom(s). PA1 (16) The liquid crystalline alkenyltolan derivative recited in paragraph (15) above wherein A.sub.2 and A.sub.4 represent 1,4-phenylene group in which a hydrogen atom(s) is not replaced by a fluorine atom(s). PA1 (17) The liquid crystalline alkenyltolan derivative recited in paragraph (15) above wherein A.sub.2 represents 1,4-phenylene group in which two hydrogen atoms are replaced by fluorine atoms and A.sub.4 represents 1,4-phenylene group in which a hydrogen atom(s) is not replaced by a fluorine atom(s). PA1 (18) The liquid crystalline alkenyltolan derivative recited in paragraph (3) above wherein G represents a covalent bond, t+m=4, and a double bond exists at a terminal of the molecule. PA1 (19) The liquid crystalline alkenyltolan derivative recited in paragraph (3) above wherein G represents a covalent bond, t+m=5, and a double bond exists at a second position counting from a terminal of the molecule. PA1 (20) The liquid crystalline alkenyltolan derivative recited in paragraph (4) above wherein X represents a chlorine atom, a bromine atom, a cyano group, or a fluoroalkyl group having 1 to 10 carbon atoms in which one or more fluoromethylene groups may be replaced by an oxygen atom(s) or an 1,2-ethenylene group(s). PA1 (21) The liquid crystalline alkenyltolan derivative recited in paragraph (4) above wherein X represents an alkyl group having 1 to 10 carbon atoms in which one or more methylene groups may be replaced by an oxygen atom(s) or an 1,2-ethenylene group(s). PA1 (22) The liquid crystalline alkenyltolan derivative recited in paragraph (21) above wherein A.sub.2 and/or A.sub.4 represents 1,4-phenylene group in which one or two hydrogen atoms may be replaced by a fluorine atom(s) and B.sub.3 represents 1,2-ethynylene group. PA1 (23) The liquid crystalline alkenyltolan derivative recited in paragraph (21) above wherein A.sub.2 and/or A.sub.3 represents an 1,4-phenylene group in which one or two hydrogen atoms may be replaced by an fluorine atom(s) and B.sub.2 represents an 1,2-ethynylene group. PA1 (24) The liquid crystalline alkenyltolan derivative recited in paragraph (23) above wherein one or two hydrogen atoms of A.sub.2 and/or A.sub.3 are replaced by an fluorine atom(s). PA1 (25) The liquid crystalline alkenyltolan derivative recited in paragraph (4) above wherein G represents a covalent bond, t+m=4, and a double bond exists at a terminal of the molecule. PA1 (26) The liquid crystalline alkenyltolan derivative recited in paragraph (4) above wherein G represents a covalent bond, t+m=5, and a double bond exists at a second position counting from a terminal of the molecule. PA1 (27) The liquid crystalline alkenyltolan derivative recited in paragraph (1) above wherein B.sub.1, B.sub.2, and B.sub.3 independently represent a covalent bond, an 1,2-ethylene, 1,2-ethynylene, oxymethylene, methylenoxy, carbonyloxy, or 1,4-butylene group. PA1 (28) A liquid crystal composition comprising at least two components and comprising at least one liquid crystalline compound recited in any one of paragraphs (1) to (27) above. PA1 (29) A liquid crystal composition comprising, as a first component, at least one liquid crystalline compound recited in any one of paragraphs (1) to (27) above, and comprising, as a second component, at least one compound selected from the group consisting of the compounds expressed by any one of the general formulas (2), (3), and (4) ##STR2## PA1 wherein R.sub.1 represents an alkyl group or alkyloxy group having 1 to 10 carbon atoms; Y represents a fluorine atom or a chlorine atom; Q.sub.1 and Q.sub.2 independently represent a hydrogen atom or a fluorine atom; r is 1 or 2; and Z.sub.1 and Z.sub.2 independently represent a covalent bond or --CH.sub.2 CH.sub.2 --. PA1 (30) A liquid crystal composition comprising, as a first component, at least one compound recited in any one of paragraphs (1) to (27) above, and comprising, as a second component, at least one compound selected from the group consisting of the compounds expressed by any one of the general formula s (5), (6), (7), (8), and (9) ##STR3## PA1 wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, and any methylene group (--CH.sub.2 --) in the alkyl or the alkenyl group may be replaced by an oxygen atom (--O--), but adjacent two or more methylene groups are not replaced by an oxygen atom(s) simultaneously; Z.sub.3 represents a covalent bond, --CH.sub.2 CH.sub.2 --, or --COO--; Q.sub.3 and Q.sub.4 independently represent a hydrogen atom or a fluorine atom; (E) represents an 1,4-cyclohexylene, 1,4-phenylene, or dioxane-2,5-diyl group; s is 0 or 1; R.sub.3 represents an alkyl group having 1 to 10 carbon atoms; Q.sub.5 represents a hydrogen atom or a fluorine atom; k is 0 or 1; R.sub.4 represents an alkyl group having 1 to 10 carbon atoms; (G.sub.1) represents an 1,4-cyclohexylene or 1,4-phenylene group; Q.sub.6 and Q.sub.7 independently represent a hydrogen atom or a fluorine atom; Z.sub.4 represents a covalent bond or --COO--; h is 0 or 1; R.sub.5 and R.sub.6 independently represent an alkyl group, alkyloxy group, or alkyloxymethyl group, each having 1 to 10 carbon atoms; (H) represents an 1,4-cyclohexylene, pyrimidine-2,5-diyl, or 1,4-phenylene group; (J) represents an 1,4-cyclohexylene or 1,4-phenylene group; Z.sub.5 represents a covalent bond, --CH.sub.2 CH.sub.2 --, --C.ident.C--, or --COO--; R.sub.7 represents an alkyl group or alkyloxy group, each having 1 to 10 carbon atoms; R.sub.8 represents an alkyl group, alkyloxy group, or alkyloxymethyl group, each having 1 to 10 carbon atoms; (K) represents an 1,4-cyclohexylene or pyrimidine-2,5-diyl group; (L) and (M) independently represent an 1,4-cyclohexylene or 1,4-phenylene group; Z.sub.6 represents a covalent bond, --CH.sub.2 CH.sub.2 --, or --COO--; Z.sub.7 represents a covalent bond, --C.ident.C--, or --COO--; and Q.sub.8 represents a hydrogen atom or a fluorine atom. PA1 (31) A liquid crystal display device including a liquid crystal composition comprising at least 2 components and comprising at least one liquid crystalline compound recited in any one of paragraphs (1) to (27) above. PA1 (32) A liquid crystal display device including a liquid crystal composition recited in any one of paragraphs (28) to (30) above.
However, the compounds expressed by the general formula (10) are not sufficiently high in .DELTA.n and dielectric anisotropy, and the compounds expressed by the general formula (11) or (12) have such defects that the viscosity of the compounds is high since they have triple bond at a lateral chain and the compounds are poor in miscibility. With respect to the compounds expressed by the general formula (13), data indicating their liquid crystallinity are not shown. Further, with respect to the compounds expressed by the general formula (14), whereas a fluorine atom(s) is introduced into a benzene ring, the increase of the value of .DELTA.n is not sufficient.